System and apparatus for controlled activation of acute use medical devices

ABSTRACT

An integrated activation system for an implantable medical device (IMD) sharing a power source, the activation system comprising a switching circuit having first and second inputs and having an output coupled to the acute use device, a gating element coupled to the first input and configured to gate power from the power source to the switching circuit, and a sensing element coupled to the second input of the switching circuit. The sensing element is configured to sense an activation condition, enable an operation interval of the switching circuit, and transmit a signal to the switching circuit during the activation condition. The switching circuit is configured to transmit power to the acute use device upon receipt of a pre-determined number of signals from the sensing element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of applicationSer. No. 10/920,818, filed Aug. 17, 2004, which claims the benefit ofU.S. Provisional Application No. 60/495,901, filed Aug. 18, 2003.

TECHNICAL FIELD

The present invention relates generally to medical devices, and moreparticularly to controlling activation of acute use medical devices.

BACKGROUND

Acute use medical devices are increasingly popular as modes forimproving medical care. For example, single-use, temporary pH sensors,recoverable miniature cameras, and leadless stimulators are some acuteuse medical devices that are becoming pervasive tools used in medicaltreatment. Most of these devices are self-contained and powered bybatteries to operate continuously until the battery is depleted or mayintermittently operate with spaced apart “sleep” intervals so as toextend battery longevity.

In designing acute use medical devices, a trade-off is commonlyencountered between competing needs for a small device size and for abattery with sufficient capacity to meet longevity goals. The battery isoftentimes the largest component in the acute use medical device andtherefore significantly impacts the size of the acute use medicaldevice.

To minimize battery size, it is generally desirable to design a devicethat draws a negligible amount of current until a deterministicactivation occurs. Such design should also be relatively immune toinappropriate activations so as to avoid unnecessary currentconsumption.

Conventional reed switches have been used in the past with implantablemedical devices and acute use medical devices. For example, aconventional reed switch has been used between the battery and thedevice circuitry of a pH sensor. As packaged, the reed switch is biasedopen (i.e., the device is “turned-off”) by an external biasing magnetplaced over the sensor during manufacture. The pH sensor is “turned-on”just prior to implantation by removing the external biasing magnet.

However, this conventional reed switch generally tends to be too largein size and thus adds significant size to the acute use medical device.Additionally, the reed switch may be susceptible to environmentaleffects (e.g., magnetic or mechanical) that may result in inappropriatesensor activation. MEMS reed switches are generally susceptible to thesame environmental effects that may cause inappropriate activation inconventional reed switches.

Other implantable device designs have used monolithic Hall effectsensors, radio frequency (RF) signaling, and ultrasound to activate thedevice. Monolithic Hall effect sensors have been used in the past tochange the state of a device based on a sensed magnetic event. Halleffect sensors typically require a stand-by current and are generallyunsuitable as a means for turning a battery-powered device on or off. Inimplementations utilizing RF signaling, the implanted device “listens”continuously for a unique RF signal. RF signaling shares a similarcurrent consumption characteristic with Hall effect sensors by generallyrequiring some current to be used while the device is in a stand-bymode. An ultrasound transducer has been used to turn on a switch thatsubsequently powers a wireless sensor containing a very small battery.In this approach, the ultrasound transducer should be in effectivecontact with a patient's body to appropriately activate the sensor.

Accordingly, it is desirable to provide an activation device for acuteuse medical devices that has relatively low or negligible current drawuntil a deterministic activation occurs. It is also desirable to providean activation device for acute use medical devices that gates current tothe devices while avoiding significant capacity drop to a shared powersource and that does not significantly contribute to an overall size ofthe device. In addition, it is desirable to provide an acute use medicaldevice having reduced susceptibility to environmental effects that mayresult in inappropriate activation thereof. Furthermore, other desirablefeatures and characteristics of the present invention will becomeapparent from the subsequent detailed description of the invention andthe appended claims, taken in conjunction with the accompanying drawingsand this background of the invention.

BRIEF SUMMARY

According to various exemplary embodiments, a system and apparatus areprovided that remotely activate implantable medical devices. In a firstexemplary embodiment, an integrated activation system is provided for anacute use medical device sharing a power source. The activation systemcomprises a switching circuit having first and second inputs and havingan output coupled to the acute use device, a gating element coupled tothe first input and configured to gate power from the power source tothe switching circuit, and a sensing element coupled to the second inputof the switching circuit. The sensing element is configured to sense anactivation condition, enable an operation interval of the switchingcircuit, and transmit a signal to the switching circuit during theactivation condition. The switching circuit is configured to transmitpower to the acute use device upon receipt of a pre-determined number ofsignals from the sensing element.

In another exemplary embodiment, an acute use medical device is providedcomprising a power source, a therapy unit, a switching circuit havingfirst and second inputs and having an output coupled to the therapyunit, a gating element having an input coupled to the power source andan output coupled to the first input of the switching circuit, and asensing element coupled to the second input of the switching circuit.The gating element is configured to gate power to the switching circuit.The sensing element is configured to change from a first state to asecond state indicating an activation condition of the acute use medicaldevice, enable an operation interval of the switching circuit, andtransmit a signal to the switching circuit during the second state. Theswitching circuit is further configured to transmit power to the therapyunit upon receipt of a pre-determined number of the signals from thesensing element.

In yet another exemplary embodiment, an integrated activation system foran acute use medical device sharing a power source is provided. Theactivation system comprises a switching circuit having a first inputcoupled to the power source and an output coupled to the therapy unitand having a second input, a gating element having an input coupled tothe power source and an output coupled to the first input of theswitching circuit, and a sensing element coupled to the second input ofthe switching circuit. The gating element is configured to gate power tothe switching circuit during a first state. The sensing element isconfigured to detect a first signal indicating an activation condition,enable an operation interval of the switching circuit, and transmit asecond signal to the switching circuit upon detecting the first signal.The switching circuit is configured to transmit power to the therapyunit upon receipt of a predetermined number of the second signals.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects and attendant advantages of theinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a block diagram illustrating an acute use medical device inaccordance with an exemplary embodiment of the present invention;

FIG. 2 is a block diagram illustrating one exemplary embodiment of theswitching circuit shown in FIG. 1;

FIG. 3 is a schematic diagram of an exemplary embodiment of a switchingcircuit; and

FIG. 4 is a block diagram illustrating another exemplary embodiment ofthe switching circuit shown in FIG. 1.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the preceding technical field,background, brief summary, brief description of the drawings, or thefollowing detailed description.

Referring to the drawings, FIG. 1 is a block diagram illustrating anacute use medical device 10 in accordance with an exemplary embodimentof the present invention. The acute use medical device 10 comprises asensing element 12, a switching circuit 14 coupled to the sensingelement 12, and a power source 16 coupled to the switching circuit 14. Atherapy Unit 18, such as a wireless pH sensor, a leadless stimulator, aminiature camera, or any number of medical devices, may be coupled tothe switching circuit 14. Although not specifically detailed herein,additional components and circuitry of acute use medical devices mayalso be included with the acute use medical device 10. The sensingelement 12 actuates the switching circuit 14 based on a desiredtriggering event. For example, if the selected therapy unit 18 is animplantable probe and the sensing element 12 is a MEMS reed switch,selective application of an external magnetic field by an operator tothe sensing element 12 activates the MEMS reed switch 12 which in turnactivates the switching circuit 14 to gate power to the implantableprobe.

The sensing element 12 is configured to detect a change in theenvironment around the sensing element 12 and is activated upon suchdetection. Changes detected by the sensing element 12 include, by way ofexample and not limitation, a physiological change (e.g., bloodchemistry pH, body temperature, etc.), a change in a magnetic field, anoptical change, or other change in the environment around the acute usemedical device 10. Examples of sensing elements 12 include but are notlimited to Micro-Electrical Mechanical systems (MEMS) reed switches,low-voltage micro-switching devices, microrelays, thermal bimorphs,photosensors, and the like. The sensing element 12 is preferably abi-stable MEMS switch. For example, the bi-stable MEMS switch comprisesa moveable beam, a support structure (e.g., a dual spring suspensionsystem) for the moveable beam, and an actuator for displacing (e.g.,lateral displacement) the moveable beam to an “ON” position from an“OFF” position.

The sensing element 12 may be selected to have a negligible current drawon the power source 16 when inactive, i.e., when not detecting apre-determined change in the environment around acute use medical device10. In one exemplary embodiment, the sensing element 12 preferably has acurrent draw of equal to or less than about 1 nanoamp (nA) from thepower source 16 when inactive, and more preferably, the sensing element12 does not draw current from the power source 16 when inactive.Providing a sensing element that draws relatively small amounts ofcurrent or no current from a battery until a deterministic activationoccurs reserves as much battery capacity for operation of the acute usemedical device 10.

The power source 16 provides current to operate the sensing element 12during activation of the same. An example of a power source includes, byway of example and not limitation, a battery. The particular current andvoltage requirements of the battery 16 may vary depending on theparticular therapy unit 18. Within such current and voltagerequirements, the battery size is selected to minimize the size of theoverall medical device 10.

In one exemplary embodiment, when the sensing element 12 is activated,the switching circuit 14 is awakened, and an operation interval, orwindow, is enabled in the switching circuit 14, such as by a timingcircuit described in greater detail hereinbelow. The switching circuit14 gates power to the therapy unit 18 to activate the therapy unit 18when a pre-determined number or a pre-determined pattern of activationsof the sensing element 12 occur within the operation interval.

For example, the switching circuit 14 may be configured to gate power tothe therapy unit 18 after three (3) activations of the MEMS reed switchoccur within the operation interval. In this example, activation of thetherapy unit 18, e.g., gating power to the therapy unit 18, does notoccur in the event that the three total activations of the MEMS reedswitch occur beyond the operation interval. Configuration of theswitching circuit 14 to gate power upon a desired number or pattern ofactivations of the sensing element 12 is suited to minimizinginterference that may occur from the environment. The switching circuit14 may be configured such that gating power to the therapy unit 18occurs on any number or pattern of pre-determined number of activationswithin the operation interval.

Referring to FIGS. 1 and 2, FIG. 2 is a block diagram illustrating oneexemplary embodiment of the switching circuit 14 shown in FIG. 1. Theswitching circuit 14 and/or sensing element 12 is selected to minimizeany capacity drop of the power source 16 during activation of either toreserve power for gating to the therapy unit 18. The life of the powersource 16 may be extended, in comparison with conventional acute usemedical devices, by minimizing the capacity drop to the power source 16that may be result from activation of the switching circuit 14 and/orsensing element 12. In one exemplary embodiment, the switching circuit14 includes a counter 20, a timer 22, and a gating element 24 coupled tothe counter 20 and the timer 22. The switching circuit 14 may beconfigured as an integrated circuit (IC) such that the counter 20, timer22, and gating element 24 are incorporated into a monolithic device. Theswitching circuit 14 or one or more portions thereof, such as thecounter 20, timer 22, and gating element 24, may also be configured asembedded instructions or programmable instructions in a microprocessoror a microcontroller contained within or coupled to the acute usemedical device 10.

The counter 20 and timer 22 are awakened by activation of the sensingelement 12. This initial activation of the sensing element 12corresponds to a new operation interval or cycle as established by thetimer 22. As previously mentioned herein, the switching circuit 14 maybe configured to gate power to the therapy unit 18. In this exemplaryembodiment, the counter 20 may be configured to count a selected orpre-determined number of sensing element 12 activations. The counter 20may include one or more latches, for example, to count sensing element12 activations.

As previously mentioned, the timer 22 establishes the operation intervalthat serves as a basis for the switching circuit 14 to determine whetherto gate power to the therapy unit 18. In one exemplary embodiment, thetimer 22 includes a resistor and capacitor circuit. The values of theresistor and capacitor determine the length of the operation interval inthis embodiment. Although latches are used to describe the counter 20and a resistor and capacitor combination is used to describe the timer22, other devices and combinations may also be used. The resultingconfiguration for the counter 20 and the timer is preferably selected tominimize impact on the overall size of the acute use medical device 10.

The gating element 24 controls power gated to the therapy unit 18. Thisgating is in response to the pre-determined number or pattern of sensingelement activations, as determined by the counter 20, occurring withinthe operation interval established by the timer 22. In one exemplaryembodiment, the gating element 24 is a transistor, such as a metal-oxidesemiconductor field effect transistor (MOSFET) or a junction type fieldeffect transistor (JFET), or a bistable MEMS switch. The transistorembodiment of the gating element 24 is suited for the monolithic deviceconfiguration of the switching circuit 14, although other types oftransistors or devices may be also used, such as discrete devices,although not specifically detailed herein.

The switching circuit 14 may additionally include a feedback circuit(not shown) or other feedback mechanism that indicates to the switchingcircuit 14 when conditions are met for discontinuing gating of power.For example, a second sensing element may be coupled with a feedbackcircuit that detects for a pre-determined condition, such as a blood pHlevel. Upon detection of the pre-determined condition, this secondsensing element is activated and triggers the feedback circuit. Thefeedback circuit in turn deactivates the switching circuit 14 todiscontinue gating of power to the therapy unit 18.

Additionally, although gating power to the therapy unit 18 is describedhereinabove with respect to activation of the sensing element 12, a morerobust system for activating the acute use medical device 10 may includeone or more conditions to be met prior to gating power. In one exemplaryembodiment, another sensing element, e.g., a third sensing element, maybe coupled to the switching circuit 14 such that the switching circuit14 gates power to the therapy unit 18 when both the pre-determinednumber or pattern of sensing element activations and the third sensingelement is activated within the operation interval. For example, thetherapy unit 18 receives power from the power source 16 when a MEMS reedswitch is activated four times and a detected temperature is about 37°C. within the operation interval.

Referring to FIGS. 1 and 3, FIG. 3 is a schematic diagram of anexemplary embodiment of a switching circuit 30. In this exemplaryembodiment, one terminal of the sensing element 12 is attached to a nodeSWITCH. The other terminal of the sensing element 12 may be coupled toground. The node SWITCH is pulled high through a resistor R₀, and acapacitor C₀ provides high frequency bypass at the node SWITCH toground. Logic NAND gates ND₀ and ND₁ form a reset-set (R-S) latch. Theoutput of ND₀ is nominally low to keep a pair of series connectedtrigger (T) flip-flops DF₁ and DF₂ in a reset mode and a capacitor C₁discharged to ground. When the output of ND₀ is high, such as atstartup, an inverter IV₀ activates a Positive-channel Metal-OxideSemiconductor (PMOS) P₀ and charges the capacitor C₁ via a resistor R₆.When voltage on C₁ reaches a switching point of an inverter IV₁, the R-Slatch resets and the output of ND₀ returns to low.

A Resistor/Capacitor (RC) element formed by R₆ and C₁ is used as part ofa timing mechanism to toggle the switching circuit 30 on/off. When thesensing element 12 activates, a high signal at the output of ND₀sensitizes a logic NOR gate NR₁ to signal level changes at the nodeSWITCH. This sensitivity lasts for an operation interval correspondingto a time for the voltage on C₁ to charge to the switch point of IV₁. Atthis point, the R-S latch resets as previously discussed hereinabove.This configuration reduces a likelihood of false state changes in a flopDF₀.

Each activation of the sensing element 12 while NR₁ is sensitized(including the initial activation of the sensing element 12) activates acounter formed by DF₁ and DF₂ from 11 to 01 to 10 to 00. The switchingcircuit 30 continuously monitors the output state of the flip-flops DF₁and DF₂ at a logic NAND gate ND₅. If the output state of the flip-flopsis 00 on a rising edge of the node SWITCH, the flop DF₀ switches states.The output of DF₀ may be buffered to drive a switch that gates currentto any additional circuit associated with the acute use medical device10. Using a falling edge of the node SWITCH to change state in thecounter and the rising edge to control DF₀ avoids races in the switchingcircuit 30 as the counter switches state.

In this exemplary embodiment, to gate power to the medical device 18 theswitching circuit 30 must sense four activations of the sensing element12. If these four activations are not sensed, the potential state changeat the output of DF₀ is abandoned and the counter resets. Quiescentcurrent consumption in this exemplary embodiment is limited to anyleakage current of the devices in the switching circuit 30.

Referring to FIGS. 1 and 4, FIG. 4 is a block diagram illustratinganother exemplary embodiment of the switching circuit 14 shown inFIG. 1. In this exemplary embodiment, the gating element 24 is coupledto a first input of the switching circuit 14, and the sensing element 12is coupled to a second input of the switching circuit 14. The gatingelement 24 gates power from the power source 16 to the switching circuit14. The switching circuit 14 transmits power to the therapy unit 18 uponthe occurrence of any pre-determined number or pattern of activations ofthe sensing element 12 within the operation interval.

In an exemplary embodiment, the sensing element 12 includes a passiveRadio Frequency Identification (RFID) Tag, or the like, that isactivated after receiving a pre-determined Radio Frequency (RF) signal.For example, an interrogation unit having a transmitter/receiver may beused to transmit a pre-determined RF signal. The RF signal powers thesensing element 12 and the gating element 24 and switches the sensingelement 12 from a non-active state to an active state. In the activestate, the RF signal, or RF codes contained with the RF signal,instructs the sensing element 12 to switch the gating element 24 to an“ON” position or active state for gating power to the switching circuit14. In an alternative embodiment, the RF signal powers the sensingelement 12 and the gating element 24, and an application of a signalhaving a pre-determined magnetic field, or a pre-determined magneticfield flux, switches the gating element 24 to the “ON” position. In thisalternative embodiment, the pre-determined magnetic field isconcurrently applied during receipt of the RF signal to gate power tothe switching circuit 14. The sensing element 12 and gating element 24are thus powered independently of the acute use medical device 10.

As previously mentioned, the counter 20 and timer 22 are awakened by theactivation of the sensing element 12, and the counter 20 counts aselected or pre-determined number of sensing element 12 activations(e.g., as indicated by receipt of the signal). The counter 20 mayinclude one or more latches, for example, to count sensing element 12activations. In another embodiment, the sensing element 12 is configuredto detect a pre-determined magnetic field change and transmit the signalto the switching circuit 14 after detecting the magnetic field change.

Although power may be gated by the gating element 24 to the switchingcircuit 14, the switching circuit 14 remains in an “OFF” state until thepre-determined number or pattern of signals from the sensing element 12(e.g., via an RFID signal or a magnetic field change) are detected.After the switching circuit 14 detects the predetermined number orpattern of signals from the sensing element 12, the switching circuit 14changes to an “ON” state to transmit power from the gating element 24 tothe therapy unit 18. The sensing element 12 and switching circuit 14thus operate to prevent inadvertent activation, such as may be invokedfrom nearby magnetic fields, of the acute use medical device 10.

Thus, there has been provided an activation device for acute use medicaldevices that has relatively low or negligible current draw until adeterministic activation occurs. An activation device for acute usemedical devices is also provided that gates current to the devices whileavoiding significant capacity drop to a shared power source and thatdoes not significantly contribute to an overall size of the device.Additionally, an acute use medical device is provided having reducedsusceptibility to environmental effects that may result in inappropriateactivation thereof.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing the exemplary embodiment or exemplary embodiments. Itshould be understood that various changes can be made in the functionand arrangement of elements without departing from the scope of theinvention as set forth in the appended claims and the legal equivalentsthereof.

1. An integrated activation system for an acute use device sharing apower source, the activation system comprising: a switching circuithaving first and second inputs and having an output coupled to the acuteuse device; a gating element coupled to said first input and configuredto gate power from the power source to said switching circuit; and asensing element coupled to said second input of said switching circuit,said sensing element configured to: sense an activation condition;enable an operation interval of said switching circuit; and transmit asignal to said switching circuit during said activation condition, saidswitching circuit configured to transmit power to said acute use deviceupon receipt of a pre-determined number of signals from said sensingelement.
 2. An activation system according to claim 1, wherein saidactivation condition comprises a pre-determined Radio Frequency (RF)signal.
 3. An activation system according to claim 1, wherein saidactivation condition comprises a pre-determined magnetic field change.4. An activation system according to claim 1, wherein said sensingelement is selected from a micro-electrical mechanical systems (MEMS)reed switch, a thermal bimorph, and a photosensor.
 5. An activationsystem according to claim 1, wherein said switching circuit comprises: acounter sub-circuit configured to count sensing element activations; anda timing sub-circuit configured to establish said operation interval;and wherein said switching circuit is configured to pass current fromsaid gating element to the acute use device when said countersub-circuit counts a pre-determined number of said signals within saidoperation interval.
 6. An activation system according to claim 1,wherein said gating element is selected from a transistor and a discreteelectronic device.
 7. An acute use medical device comprising: a powersource; a therapy unit; a switching circuit having first and secondinputs and having an output coupled to said therapy unit; a gatingelement having an input coupled to said power source and an outputcoupled to said first input of said switching circuit, said gatingelement configured to gate power to said switching circuit; and asensing element coupled to said second input of said switching circuit,said sensing element configured to: change from a first state to asecond state indicating an activation condition of the acute use medicaldevice; enable an operation interval of said switching circuit; andtransmit a signal to said switching circuit during said second state,said switching circuit further configured to transmit power to saidtherapy unit upon receipt of a pre-determined number of said signalsfrom said sensing element.
 8. An acute use medical device according toclaim 7, wherein said sensing element is further configured to changefrom said first state to said second state upon a magnetic field change.9. An acute use medical device according to claim 7, wherein saidsensing element is further configured to change from said first state tosaid second state upon receipt of a Radio Frequency (RF) signal.
 10. Anacute use medical device according to claim 7, wherein said therapy unitis a miniature camera.
 11. An acute use medical device according toclaim 7, wherein said therapy unit is a stimulator.
 12. An acute usemedical device according to claim 11, wherein said therapy unit is asensor.
 13. An acute use medical device according to claim 7, whereinsaid sensing element is selected from a micro-electrical mechanicalsystems (MEMS) reed switch, a thermal bimorph, and a photosensor.
 14. Anacute use medical device according to claim 7, wherein said switchingcircuit comprises: a counter sub-circuit configured to count sensingelement activations; and a timing sub-circuit configured to establishsaid operation interval.
 15. An acute use medical device according toclaim 14, wherein said counter sub-circuit comprises at least one latchdevice and at least one T flip-flop device.
 16. An acute use medicaldevice according to claim 7, wherein said sensing element is furtherconfigured to draw zero current from said power source during said firststate.
 17. An acute use medical device according to claim 17, whereinsaid pre-determined condition is selected from a pre-determined timeinterval, a pH value, and a power source voltage.
 18. An integratedactivation system for an acute use device sharing a power source, theactivation system comprising: a switching circuit having a first inputcoupled to the power source and an output coupled to said therapy unitand having a second input; a gating element having first and secondinputs and an output, said first input of said gating element coupled tosaid power source, said output of said gating element coupled to saidfirst input of said switching circuit, said gating element configured togate power to said switching circuit during a first state; and a sensingelement coupled to said second input of said switching circuit and saidsecond input of said gating element and configured to: detect a firstsignal indicating an activation condition; enable an operation intervalof said switching circuit; and transmit a second signal to saidswitching circuit upon detecting said first signal, said switchingcircuit configured to transmit power received from said gating elementto said therapy unit upon receipt of a predetermined number of saidsecond signals.
 19. An integrated activation system according to claim18, wherein said activation condition is a pre-determined RF signalhaving an RF code, and wherein said sensing element is furtherconfigured to switch said gating element to said first state upondetecting said RF code, said pre-determined RF signal powering saidsensing element and said gating element.
 20. An integrated activationsystem according to claim 18, wherein said activation condition is apre-determined RF signal, wherein said pre-determined RF signal powerssaid sensing element and said gating element, and wherein said gatingelement is further configured to switch to said first state upondetecting a signal having a pre-determined magnetic field.